Department of Neurology, Inselspital, Bern University Hospital and University of Bern, Bern, Switzerland.
Department of Neurosurgery, Inselspital, Bern University Hospital and University of Bern, Bern, Switzerland.
J Neurophysiol. 2021 Sep 1;126(3):736-742. doi: 10.1152/jn.00213.2021. Epub 2021 Jul 21.
The technique of multifiber muscle velocity recovery cycle recordings was developed as a diagnostic tool to assess muscle membrane potential changes and ion channel function in vivo. This study was undertaken to assess the impact of intermittent high-frequency stimulation on muscle velocity recovery cycle components and to study whether the changes can be modified by endurance training. We recorded muscle velocity recovery cycles with 1 and 2 conditioning stimuli in the left tibialis anterior muscle in 15 healthy subjects during intermittent 37-Hz stimulation and analyzed its effects on the different phases of supernormality. Recordings were conducted before and after 2-wk endurance training. Training effect was assessed by measuring the difference in endurance time, peak force, and limb circumference. Muscle velocity recovery cycle recordings during intermittent high-frequency stimulation were successfully recorded in 12 subjects. Supernormality for interstimulus intervals shorter than 15 ms (early supernormality) was maximally reduced at the beginning of repetitive stimulation and recovered during stimulation. Supernormality for interstimulus intervals between 50 and 150 ms (late supernormality) showed a delayed decrease and stayed significantly reduced after high-frequency stimulation. Training had no significant effect on any of the measured parameters, but we found that training induced changes in peak force correlated positively with baseline changes of early supernormality. Our results support the hypothesis that early supernormality represents membrane potential, which depolarizes in the beginning of high-frequency stimulation. Late supernormality probably reflects transverse tubular function and shows progressive changes during high-frequency stimulation with delayed normalization. A conditioning impulse in human muscle fibers induces a prolonged phase of increased velocity (also called supernormality) with two phases related to an early and late afterpotential. We investigated the effects of intermittent 37-Hz stimulation on muscle fiber supernormality and found that the early and late phases of supernormality changed differently, and that the late phase may reflect the ionic interactions responsible for the counter-regulation of muscle fatigue.
多纤维肌速度恢复周期记录技术被开发为一种诊断工具，用于评估体内肌肉膜电位变化和离子通道功能。本研究旨在评估间歇性高频刺激对肌肉速度恢复周期成分的影响，并研究这些变化是否可以通过耐力训练来改变。我们在 15 名健康受试者的左胫骨前肌中记录了 1 个和 2 个条件刺激的肌肉速度恢复周期，分析了其对超极化不同阶段的影响。在 2 周的耐力训练前后进行了记录。通过测量耐力时间、峰值力和肢体周长的差异来评估训练效果。在 12 名受试者中成功记录了间歇性高频刺激期间的肌肉速度恢复周期记录。短于 15ms 的刺激间隔（早期超极化）的超极化在重复刺激开始时最大程度地减小，并在刺激过程中恢复。50 至 150ms 之间的刺激间隔（晚期超极化）的超极化表现出延迟的减少，并在高频刺激后仍然显著降低。训练对任何测量参数均没有显著影响，但我们发现，峰值力的训练诱导变化与早期超极化的基线变化呈正相关。我们的结果支持这样的假设，即早期超极化代表在高频刺激开始时去极化的膜电位。晚期超极化可能反映横管功能，并在高频刺激过程中表现出进行性变化，延迟正常化。在人类肌纤维中，一个条件刺激会引起速度增加的延长相（也称为超极化），有两个与早期和晚期后电位相关的相。我们研究了间歇性 37Hz 刺激对肌纤维超极化的影响，发现超极化的早期和晚期阶段变化不同，晚期阶段可能反映了负责肌肉疲劳反调节的离子相互作用。
